Electron devices and light-emitting-devices having a Group III-V compound semiconductor are well-known. In particular, there have been practically used as a light-emitting-device an AlGaAs or AlGaInP material formed on a GaAs substrate for red luminescence and a GaAsP material formed on a GaP substrate for orange or yellow luminescence. An infrared light-emitting-device using an InGaAsP material on an InP substrate is also known.
As the types of these devices, a light-emitting diode utilizing spontaneous emissive light (light-emitting diode: LED), a laser diode having an optical feedback function for deriving an induced emissive light (laser diode: LD) and a semiconductor laser are known. These devices have been used as, for example, a display device, a communication device, a light-source device for high-density optical recording, a device for high-precision optical processing and a medical device.
Since 1990s, as results of attempts for research and development of an InxAlyGa(1-x-y)N Group III-V compound semiconductor (0≦x≦1, 0≦y≦1, 0≦x+y≦1) containing nitrogen as a Group V element, the emission efficiency of the devices using the same has been significantly improved, and blue and green LEDs with high efficiency have been realized. Subsequent research and development have led to LEDs with high efficiency even in the ultraviolet region and recently blue LEDs have been marketed.
By integrating a phosphor with an ultraviolet or blue LED as an excitation light source, a white LED can be obtained. Since a white LED may be utilized as a next-generation lighting device, improvement in output and efficiency in an ultraviolet or blue LED to be an excitation light source has considerably higher industrial significance. At present, intense attempts are made for improving efficiency and output in a blue or ultraviolet in the light of applications in LED lighting.
For improving an output in an element, that is, improvement of the total radiation flux, increase of an element size and ensuring resistance to a large input power are essential. In addition, a common LED is a point light source. If adequately enlarged, the element exhibits light-emitting properties as a plane light source, which becomes particularly suitable for illumination applications.
However, an element having geometrical similarity with simply enlarged area of a common small LED does not exhibit uniform emission intensity over the whole element in general. Thus, it may be conceivable that a plurality of elements are aligned on a substrate. For example, Japanese Laid-open Patent Publication No. 1999-150303 (Patent Reference 1), Japanese Laid-open Patent Publication No. 2001-156331 (Patent Reference 2), Japanese Laid-open Patent Publication No. 2002-26384 (Patent Reference 3) and Japanese Laid-open Patent Publication No. 2003-115611 (Patent Reference 4) have described that a plurality of LEDs are formed over one substrate.
Japanese Laid-open Patent Publication No. 1999-150303 (Patent Reference 1) has disclosed an integrated light-emitting component where a plurality of LEDs are connected in series over a substrate. In this reference, in order to separate a part having a pair of pn junction, i.e. a single light-emitting-unit, completely electrically, a GaN layer is etched using an Ni mask until the insulative substrate is exposed (see, paragraph 0027). Therefore, each light-emitting-unit is just a separate LED formed on the same substrate. As shown in FIG. 6 of this Patent Reference 1, a separation trench separating light-emitting-units does not emit light and thus the configuration is a simple alignment of light-emitting elements and is not a surface light source having higher uniformity of emission intensity. In such a configuration, deterioration of one light-emitting-unit in the integrated elements leads to extreme reduction in an emission intensity only in that area. In terms of the manufacturing process, in a process where a GaN material is dry etched using a metal mask such as Ni, controlling an etching shape is not satisfactory because the metal mask is not necessarily adequately resistant and thus the selection ratio in dry etching of GaN material is insufficient.
Japanese Laid-open Patent Publication No. 2001-156331 (Patent Reference 2) has also described an integrated device where a plurality of light-emitting-units are formed over one substrate. However, in this reference, the light-emitting-units having a pair of pn junction are also mutually completely separated by a separation trench, and therefore they are separate LEDs formed on the same substrate, as shown in FIG. 2. Therefore, the separation trench (a method for forming it is not disclosed) separating the light-emitting-units does not emit a light, so that emission intensity uniformity cannot be ensured over the whole surface light source. In such a configuration, deterioration of one light-emitting-unit in the integrated elements leads to extreme reduction in an emission intensity only in that area.
Japanese Laid-open Patent Publication No. 2002-26384 (Patent Reference 3) has disclosed a process for LED integration for the purpose of providing an integrated nitride semiconductor light-emitting element with a large area and a higher light-emission efficiency. However, as described in FIGS. 2 and 3 and paragraph 0038 in the reference, a separation trench between a light-emitting-unit and another light-emitting-unit is formed by etching a semiconductor layer until the etching reaches a sapphire substrate by RIE using SiO2 as a mask. Since the separation trench separating the light-emitting-units does not emit a light, emission intensity uniformity cannot be ensured over the whole surface light source similar to Patent References 1 and 2. Furthermore, deterioration of one light-emitting-unit in the integrated elements leads to extreme reduction in an emission intensity only in that area. In addition, since SiO2 is used as an etching mask (an oxide mask or a nitride mask is not necessarily resistant) in the process for forming the separation trench, a selection ratio in etching GaN material is insufficient and shape controlling during etching is difficult.
Japanese Laid-open Patent Publication No. 2003-115611 (Patent Reference 4) has disclosed a light-emitting-device in which LEDs are integrated for using as a plane light-emitting light source or display. This reference describes two types of devices, in one of which light-emitting-units having a pair of pn junction are mutually electrically separated (Claim 4, FIG. 10(b) and so on). Separation between them is formed by dicing (FIG. 10). In this type, as in the above three references, emission intensity is reduced in a separation trench between light-emitting-units so that uniformity cannot be ensured over the whole surface light source. Likewise, deterioration in one light-emitting-unit leads to extreme reduction in an emission intensity only in that adjacent area. The second type device described in this reference is a device where light-emitting-units having a pair of pn junction are mutually electrically connected (see, Claim 5, FIG. 10(a) and so on). In this type, an n-type semiconductor layer is common to the whole light-emitting-device (FIG. 10(a)). In such a case, current flows not only into the nearest p-side electrode from an n-side electrode but also into all the p-side electrodes from one n-side electrode, so that current injection efficiency is not high as the whole light-emitting-device. Furthermore, since all the p-side electrodes are electrically connected to all the n-side electrodes, deterioration in one part leads to deterioration in the whole device. Therefore, this type device is essentially unsuitable to increase an area for providing a plane light source.    Patent Reference 1: Japanese Laid-open Patent Publication No. 1999-150303    Patent Reference 2: Japanese Laid-open Patent Publication No. 2001-156331    Patent Reference 3: Japanese Laid-open Patent Publication No. 2002-26384    Patent Reference 4: Japanese Laid-open Patent Publication No. 2003-115611